SOLUTION: Q. Prove the following identity: 1 divided by 1+cosx = 1/sin^2x - 1/sinxtanx I am at the dead end but these are my steps: R.S. 1 divided by(sinx)(sinx)-1 divided by (sinx)(sinx

Algebra ->  Quadratic Equations and Parabolas -> SOLUTION: Q. Prove the following identity: 1 divided by 1+cosx = 1/sin^2x - 1/sinxtanx I am at the dead end but these are my steps: R.S. 1 divided by(sinx)(sinx)-1 divided by (sinx)(sinx      Log On


   



Question 5053: Q. Prove the following identity: 1 divided by 1+cosx = 1/sin^2x - 1/sinxtanx
I am at the dead end but these are my steps:
R.S.
1 divided by(sinx)(sinx)-1 divided by (sinx)(sinx/cosx)=
sin^2x+cos^2x divided by sin^2x - sin^2x+cos^2xdivided by (sin^2x/cosx)=
(sinx)(sinx)+(cosx)(cos)divided by (sinx)(sinx) - (sinx)(sinx) + (cosx)(cosx)(cosx)divided by (sinx)(sinx)=
sin^2x + cos^2x - sin^2x + cos^2x(cosx) divided by (sinx)(sinx)=
and here either
1 - cosx divided by sin^2x
or
2cos^2x(cosx)divided by sin^2x
--------
thanks mmm

Answer by longjonsilver(2297) About Me  (Show Source):
You can put this solution on YOUR website!
in any proof, pick one of the 2 sides and manipulate it until you get the other side. Always start with the more complicated side too!

Looking at your proof: 1%2F%281%2Bcosx%29+=+1%2F%28sin%5E2%28x%29%29+-+1%2F%28sinxtanx%29, the RighHand side looks more complicated, so i shall pick this..basically i have more things to work with...

1%2F%28sin%5E2%28x%29%29+-+1%2F%28sinxtanx%29. I shall use the facts that tanx = sinx/cosx and also sin%5E2%28x%29+%2B+cos%5E2%28x%29+=+1.

1%2F%28sin%5E2%28x%29%29+-+1%2F%28sinx%2Asinx%2Fcosx%29
1%2F%28sin%5E2%28x%29%29+-+cosx%2F%28sin%5E2%28x%29%29
%281+-+cosx%29%2F%28sin%5E2%28x%29%29
%281+-+cosx%29%2F%281+-+cos%5E2%28x%29%29. Now factorise the denominator:

%281+-+cosx%29%2F%28%281+-+cosx%29%281+%2B+cosx%29%29
1%2F%281+%2B+cosx%29 QED

jon.